1. Field of the Invention
The present invention generally relates to multi-piece golf balls having a multi-layered solid core and cover of at least one layer. In one preferred embodiment, a five-piece ball is formed. The center of the core is made of a thermoset rubber material. Three intermediate layers of thermoplastic material enclose the center. The outer cover layer is made of a composition comprising a polyurethane, polyurea, or copolymer or blend thereof.
2. Brief Review of the Related Art
Multi-piece, solid golf balls are used today by recreational and professional golfers. Basically, these golf balls contain an inner core protected by a durable cover. The core and cover may be single or multi-layered. For example, three-piece golf balls having an inner core, an inner cover layer, and an outer cover layer may be used. In other instances, golfers will use a four-piece ball containing a dual-core (inner core and surrounding outer-core layer) and dual-cover (inner cover layer and surrounding outer cover layer). Five and six-piece balls may be made with intermediate layer(s) disposed between the inner core and outer cover. Normally, the core is made of a natural or synthetic rubber material such as, for example, styrene butadiene, polybutadiene, or polyisoprene; and the cover is made of a durable material such as, for example, ethylene acid copolymer ionomer resins, polyamides, polyesters, polyurethanes, or polyureas. Today, the industry is interested, among other things, in making balls that can rebound faster, retain more total energy when struck with a club, and have longer flight distance.
In recent years, golf ball manufacturers have looked to developing multi-layered core and cover constructions. Golf balls containing multi-layered cores and covers are generally described in the patent literature. For example, Bulpett et al, US Patent Application Publication US 2009/0227394 discloses multi-layered core construction comprising: a) an inner core formed from a first thermoset rubber composition; b) an intermediate core layer formed from a partially-neutralized or highly-neutralized ionomer composition; and c) an outer core formed from a second thermoset rubber composition. A cover layer having a thickness of about 0.01 to 0.05 inches and a surface hardness of about 60 Shore D or less is formed around the core.
Sullivan et al., US Patent Application Publication No. US 2009/0017940 discloses golf balls having a dual-core and a single-layered cover. The dual-core includes an inner core formed from a rubber composition and an outer core layer formed from a highly neutralized polymer (HNP) composition comprising an ethylene acid copolymer. In the HNP composition, at least 80% of all acid groups are neutralized. The inner core has an outer surface hardness of less than 80 Shore C; the outer core layer has an outer surface hardness of 56 Shore D or greater; and the cover layer has a material hardness of 60 Shore D or less.
Sullivan et al., U.S. Pat. Nos. 7,357,736 and 7,211,008 disclose golf balls comprising: a) an inner core layer formed from a diene rubber composition; (b) an outer core layer formed from a high modulus highly neutralized polymer (HNP) comprising a highly neutralized ethylene/(meth)acrylic acid copolymer having a modulus of from 45,000 psi to 150,000 psi; (c) an intermediate core layer disposed between the inner core layer and the outer core layer and formed from a low modulus HNP composition comprising a highly neutralized ethylene/(meth)acrylic acid/alkyl (meth)acrylate copolymer having a modulus of from 1,000 psi to 50,000 psi. In the HNP compositions, at least 80% of all acid groups are neutralized.
Higuchi et al., U.S. Pat. No. 7,226,367 discloses a golf ball comprising a solid core consisting of a center core and outer core, wherein at least one of the core layers is made of a rubber composition, and wherein the center core has a JIS-C hardness of 40 to 60 on its center and a JIS-C hardness of 55 to 75 on its surface.
Nesbitt et al., U.S. Pat. No. 7,147,578 discloses golf balls containing a dual-core. The inner core (center) and outer core layer may be formed from a thermoset material or a thermoplastic material. The '578 patent discloses suitable thermoset materials as including polybutadiene or any natural or synthetic elastomer, metallocene polyolefins, polyurethanes, silicones, polyamides, and polyureas. Suitable thermoplastic materials are described as including ionomers, polyurethane elastomers, and combinations thereof.
Higuchi et al., U.S. Pat. No. 7,086,969 discloses a multi-piece golf ball comprising dual-core having a center and outer core layer; and a dual-cover having an inner cover layer and outer cover layer. The center is made from a rubber composition and has a JIS-C hardness of 40 to 60 in its center and a JIS-C hardness of 55 to 75 on its surface. The outer core also is made of rubber and has a JIS-C surface hardness of 75 to 95. The inner cover layer has a Shore D hardness of 50 to 80, and the outer cover layer has a Shore D hardness of 35 to 60.
Iwami, U.S. Pat. No. 6,987,159 discloses a solid golf ball with a solid core and a polyurethane cover, wherein the difference in Shore D hardness between a center portion and a surface portion of the solid core is at least 15, the polyurethane cover has a thickness (t) of not more than 1.0 mm and is formed from a cured urethane composition having a Shore D hardness (D) of from 35 to 60, and a product of t and D ranges from 10 to 45.
Higuchi et al., U.S. Pat. No. 6,786,836 discloses a golf ball comprising a solid core and cover, wherein the core is a hot-molded product of a rubber composition, and the cover is primarily composed of thermoplastic or thermoset polyurethane elastomer, polyester elastomer, ionomer resin, polyolefin elastomer, or mixtures thereof.
Iwami, U.S. Pat. No. 6,686,436 discloses a golf ball having a solid core made of rubber and a polyurethane cover, wherein the difference in Shore D hardness between a center portion and a surface portion of the solid core is at least 15, and the polyurethane cover is obtained by curing a composition comprising an isocyanate group-terminated urethane prepolymer and aromatic polyamidne compound.
Watanabe, U.S. Pat. No. 6,679,791 discloses a multi-piece golf ball which includes a rubbery elastic core, a cover having a plurality of dimples on the surface thereof, and at least one intermediate layer between the core and the cover. The intermediate layer is composed of a resin material which is harder than the cover. The elastic core has a hardness which gradually increases radially outward from the center to the surface thereof. The center and surface of the elastic core have a hardness difference of at least 18 JIS-C hardness units.
Higuchi et al., U.S. Pat. Nos. 6,634,961; 7,086,969; and 7,153,224 disclose a multi-piece golf ball comprising a solid core consisting of a center core and outer core; and an inner cover and outer cover layer, wherein the solid core is molded from a rubber composition containing polybutadiene rubber; another diene rubber; an unsaturated carboxylic acid; an organo-sulfur compound; an inorganic filler; and an organic peroxide.
Yamagishi et al., U.S. Pat. No. 5,782,707 discloses a three-piece solid golf ball consisting of a solid core, an intermediate layer, and a cover, wherein the hardness is measured by a JIS-C scale hardness meter, the core center hardness is up to 75 degrees, the core surface hardness is up to 85 degrees, the core surface hardness is higher than the core center hardness by 8 to 20 degrees, the intermediate layer hardness is higher than the core surface hardness by at least 5 degrees, and the cover hardness is lower than the intermediate layer hardness by at least 5 degrees.
Although some conventional multi-layered core and cover constructions are generally effective in providing golf balls having good playing properties, there is a continuing need for improved core and cover constructions in golf balls. Particularly, there is a need for balls having high resiliency and other properties that will allow players to generate higher initial ball speed and less initial ball spin when driving the ball off the tee. This will allow players to achieve longer distance on their driver shots. The present invention provides multi-layered golf balls having such properties as well as other advantageous features and benefits.